This invention relates to medical equipment, in particular for the diagnosis of respiratory problems.
Asthma and respiratory diseases are becoming widespread health problems. Various causes have been speculated, such as indoor and outdoor air pollution. Diesel-powered vehicles are known to produce particulates harmful to the lungs. Modern houses are usually well sealed and insulated, and in consequence may have high levels of indoor air pollution due to vapors such as formaldehyde exuding from carpets.
Asthma diagnosis is often achieved by measuring one or more respiratory parameters, for example, peak flow and forced exhaled volume in one second (FEV1). Diagnosis may be achieved using the variety of instruments known in the art. For example, peak flow is often measured using mechanical devices. However, existing devices may not provide the combination of flow profile data and breath parameters necessary for improved diagnosis. The volume and flow rate of inhaled or exhaled breath may be monitored using a respiratory spirometer. For spirometry, it is useful to monitor the total oxygen consumption of the patient.
Respiratory analysis can be used to diagnose lung disease, lung cancer, and other airway diseases. The presence of nitric oxide in the breath of a person is often of diagnostic significance. Several volatile organic compounds have been correlated with lung cancer. Bacterial infection of the lungs may be detected using antibody response to pathogens in exhaled breath. Thus, there exists a diagnostic need for a calorimetry system capable of readily measuring respiratory characteristics and components.
Resting metabolic rate is an important factor in the calorie balance of a person. A person""s total energy expenditure (TEE) is equal to the sum of resting energy expenditure (REE) and activity-related energy expenditure (AEE), i.e.:
TEE=REE+AEE 
The calorie balance for a person is the difference between the total energy expenditure and caloric intake. As part of a weight control program, a person might record caloric intake, and estimate or determine activity levels using accelerometers, pedometers, and the like. However, unless the person has accurate knowledge of REE, weight loss predictions are not possible. REE is a larger component of TEE than AEE, so that an accurate knowledge of REE is essential in calculating calorie balance. One problem in a weight control program is that REE usually falls during a diet, due to the body""s natural response to perceived starvation. Hence, even significantly reducing calorie intake may not be enough to lose weight.
Obesity is a huge problem, particularly in the developed world. Many medical problems are correlated with obesity, e.g. heart problems, joint problems, etc. Hence, it is useful to a physician to assist a patient with a weight control program using an indirect calorimeter to determine metabolic rate. The current medical system often does not emphasize disease prevention; however, this may change in the near future. A physician may therefore wish to play a greater role in disease prevention, in which case professional assistance with weight control becomes important.
There are formulas in the literature (e.g. the Harris-Benedict equation) which allow calculation of metabolic rate from height and weight. If metabolic rate is significantly higher or lower than a normal range, based on such a formula, this can be diagnostic of a range of metabolism-based problems. Hence, there exists a need for a physician to measure metabolic rate of a person, as part of a diagnostic test for medical problems.
An indirect calorimetry system includes a plurality of transducers sensitive to expired airflow from a subject""s lungs. A calorimetry housing encloses the plurality of transducers. The transducers"" output is communicated to a microprocessor that calculates expiration characteristics and conveys those characteristics to a graphical display. In another embodiment, an indirect calorimetry system includes a plurality of transducers sensitive to expired airflow and a housing enclosing the transducers. A microprocessor in communication with the transducers calculates expiration characteristics and those characteristics are communicated by way of a communication link to devices such as a computer, a communication network such as the Internet or to a PDA.
A process for monitoring physiological gas exchange associated with respiration includes the active expiring into an indirect calorimeter for a period of time and then measuring the expiration flow with a plurality of transducers. The measurement of expiration flow is then time stamped and displayed as a function of the period of time.